1. Field of the Invention
The present invention relates to an apparatus and method for processing a video signal. In particular, the invention relates to a video signal processing apparatus such as an electronic still camera or a video camera which has a liquid crystal monitor, and which is operated exclusively by battery driving, and a video signal processing method for use therein.
2. Related Background Art
A video signal processing apparatus of this sort is described in JP 10-336494 A. An image of a desired object is captured by a solid-state image pickup device and then an image signal representing the object image is converted into digital image data to be recorded in a recording medium such as a memory card. Then, the recorded image data can be arbitrarily read out so that the image represented by the image data can be reproduced on a liquid crystal monitor which is mounted on the apparatus.
As for such a digital camera, there is known one in which an image in a subject area can be enlarged and displayed during reproduction, and JP 10-336494 A discloses a digital camera with a zoom display function. That is to say, this type of digital camera includes two frame memories: a first frame memory for storing image data of a reproduced image; and a second frame memory for storing a selection frames used to select a subject area. The selection frame is displayed so as to be superimposed on the reproduced image. If a user selects a selection frame of a desired magnification to move the selection frame to a subject area, then the image is enlarged onto the first frame memory by the pixel interpolation method to be displayed on a liquid crystal monitor.
However, in the conventional digital camera, the contents of the frame memory are updated whenever an image is enlarged. Thus, a period of time required for a memory access and an enlargement processing which are caused every time an image is enlarged is felt as a stress by a user who is enlarging an image while checking a state of the magnification. In addition, an excessive electric power is consumed every time an image is enlarged. Moreover, the frame memory is a display memory for the liquid crystal monitor, and hence an image on the frame memory is rougher than that of a captured image. Nevertheless, since in this digital camera, an enlarged image is obtained by enlarging and interpolating a rough image on the frame memory to construct a new frame memory, an image after determination of the magnification is considerably rough.
In addition thereto, when an image which was enlarged once is to be reduced, it is necessary to newly reconstruct a frame memory through the expansion of the compressed image data of the original image and further enlarge the reconstructed image. In this case, it takes a longer processing time and larger power consumption as compared with the case of enlargement of an image.